Collection Framework - SortedSet, NavigableSet and TreeSet

-
SortedSet is a interface that extends the Set interface.

As the name suggests, it contains certain methods specific to sorting. Duplicates not allowed, insertion order not preserved.

Elements are stored in a sorted manner. For integers, they are stored in ascending order. For Strings, its alphabetical order. Custom objects need to implement Comparable interface.

SortedSet has the following methods :

first() - returns first element
last() - returns last element
headSet(median) - returns elements before the median element
tailSet(median) - returns elements after the median element alongwith median element
subSet(startElement, lastElement) - set of elements inclusive startelement excluding lastElement
comparator() - returns comparator if you  have set a different rule for sorting. default null if you havent used any sorting.

Now we also need the facility to navigate through the elements, and for this NavigableSet was introduced. It extends the SortedSet and in addition brings the navigation methods :

lower(element) - returns the element less than the specified element
floor(element) - returns the element less than or equal to specified element
ceiling(element) - returns >= element to the specified element
higher(element) - returns > element to the specified element
pollFirst() - retreive and remove the first element
pollLast() - retreive and remove the last element

All the above methods return null if no such element found.

The implemention class is the TreeSet.
TreeSet is implemented based on underlying data structure as balanced tree. Objects are inserted based on a sorting order either natural or as specified. Since sorting is involved, we cannot have different types of elements stored. all elements should be of same type.

TreeSet has the following constructors :

TreeSet() - creates tree set with default sorting order
TreeSet(Comparator com) - creates tree set with sorting specifed by comparator
TreeSet(Collection coll) - creates tree set from collection with default sorting order
TreeSet(SortedSet set) - creates tree set from collection with sorting as per specified set

An example for TreeSet can be found here

Comments

Post a Comment

Popular posts from this blog

Collection Framework - HashSet And LinkedHashSet class

-
As ArrayLists use arrays as the underlying storage, in case of HashSet, hashtable is the datastructure that was implemented. HashSet stores objects based on their hashcodes. Duplicates are not allowed and since its stored based on hashcode, insertion order is not preserved. Hashing data structures comes with a initial capacity of 16  i.e. 2 power 4. There is one more terminology with regards to hashing data structures, load factor , i.e. when should a new hashset be created with double the capacity. Default load factor is 0.75 i.e. when 75% hashset is filled, a new larger hashset is created. HashSet comes with the following constructors : HashSet() - creates a hash set with a default initial capacity of 16 and load factor 0.75 HashSet(int initialCapacity) - creates a hash set with the specified initial capacity and load factor 0.75. HashSet(int initialCapacity, int loadFactor) - creates a hash set with the specified initial capacity and the specified load factor HashSet(
Read more

Collection Framework - Cursors in Java

-
Java provides interfaces that are implemented by collection classes so that we can fetch elements one by one or iterate through the elements in the collection. The cursors provided by Java are : 1. Enumeration 2. Iterator 3. ListIterator 4. SplitIterator(introduced in Java 8) Before the introduction of cursors, what was the way we used to iterate through the collection? The traditional for loop!!! for(int i=0; i< coll.size;i++) {      System.out.println(coll.get(i)); } Enumeration It is a legacy interface that provides us the facility to traverse through the elements of the legacy classes one by one. The example for enumeration can be found  here Iterator Enumeration has 2 limitations : 1. Its only applicable to legacy classes 2. We do not have an option to remove element from collection while traversing The above two limitations were overcome by introduction of Iterator. Iterator is a universal cursor i.e. it is applicable to all the classes in the collecti
Read more

Hashed data structures

-
Image
Introduction Common way of indexing data is by using hash maps which we use to map keys to values. The indexing of keys to values is built by using a hash function to compute which bucket or location our data will be stored in. If two pieces of data are hashed to the same location, it is called "collision". The Hash Function A hash function is basically a function that takes arbitrary data and returns a fixed length output. We usually call the output of a hash function as hash code. It is one of the most widely used data structures in modern programming. Properties of a hash function : 1. Deterministic :- A given input always generates the same output 2. Uniform :- The output should be probable in a given range  public long DJBHash(String str)    {       long hash = 5381;       for(int i = 0; i < str.length(); i++)       {          hash = ((hash << 5) + hash) + str.charAt(i);       }       return hash;    } Perfect Hashing
Read more